This invention relates to preventing delamination between joined materials which have different thermal coefficients of expansion. Specifically, the invention relates to providing a fiber based interface reinforcement between two dissimilar materials that are to be joined. Even more specifically, this invention relates to unique fibers and their use in joining dissimilar materials.
A long standing problem that is present in many fields where a structure is constructed or components are assembled from materials having different thermal coefficients of expansion is how to compensate for the difference. Such a structure may be a roof, a pipeline, concrete highway or bridge, nose cone for a rocket or an assembly of parts for a space craft.
When materials having different thermal coefficients of expansion are joined without provision for the expansion, the result can be wrinkling, buckling, delamination, rupture and even collapse. Typically, expansion joints are provided with cushioning or stress and force absorbing elastomeric fillers. Joints have to be especially designed to compensate for expansion and contraction as ambient temperatures vary constantly. Accordingly, it is a primary object of the present invention to provide a novel method and product to deal with and compensate for the difference in thermal coefficients of expansion between dissimilar materials that are joined.
In space craft today, two differing materials which may be joined are carbon panels or parts to quartz panels or parts. These parts may be planar in configuration or they may have complex curves and bends. The different coefficients of thermal expansion make it difficult to achieve a secure joining of the materials. Accordingly, it is another object of the present invention to provide a satisfactory method and means for joining quartz components with carbon components.
Applicant""s unique and surprising solution to the foregoing mentioned problems are described in the Summary of Invention and Detailed Description which follow.
In one aspect the invention is a method of joining a first and second dissimilar materials by blending the first and second materials to form a composite which has a coefficients of expansion intermediate of the two materials. The composite material can then be adhesively joined to a respective surface of the first and second dissimilar material at and in the interface to form a sandwich construction:
First material/Composite/Second material
High strength adhesives such as those based on epoxy resins are well known to those skilled in the art are used to adhere to composite to the first and second interface surfaces.
The foregoing aspect of the invention is adaptable to materials which blend compatibly such as polymeric and metallic materials that are mutually soluble in each other and/or and can be melt blended to form true mixtures or compounds and which include blends, suspensions, and alloys. However, not all materials can be readily blended by melt or solution blending. Accordingly, another aspect of the invention is described below.
In a second aspect of our invention, fibrils or fibers of the dissimilar materials are blended in strands or bundles which can be twisted and spun into yarn and then woven or braided into a fabric or composite yarn. This blended yarn may be the sandwiched portion between joined interfaces and surrounded with an adhesive which joins the material surfaces in the interface. The yarn or fabric within the adhesive acts as a reinforcement much the same way that concrete is reinforced by re-bars.
In still another aspect, carbon fibers may be twisted with quartz fibers to form a strand wherein the amount of carbon and quartz in the twisted yarn can be varied to provide a compatible composite coefficient of thermal expansion depending on the size and configuration of the quartz and carbon components being joined. The composite yarn may be woven into a fabric to reinforce the joint or braided into a mini-cable to fit within a joint. The selection of the configuration of the composite structure depends on the geometry of the joint being joined.
The invention will be better understood and appreciated by the drawings and detailed description which follow.